Optical disc molding apparatus

ABSTRACT

An optical disc molding apparatus is able to mold an optical disc in which the occurrence of swollen portions of trumpet shape on the upper and lower surfaces of on the outer peripheral portion of a disc base may be minimized and in which a burr may be prevented from being produced on the outer peripheral portion of the disc base. In the optical disc molding apparatus having a ring ( 6 ) for molding an outer diameter portion of a disc base and holding a stamper ( 5 ) for transfer a signal pit, a holding surface of the ring ( 6 ) for holding the stamper ( 5 ) is formed as the concave and convex surfaces comprising a plurality of concentric land portions ( 21 ) and a plurality of concentric groove portions ( 22 ). The outer peripheral surface of the stamper ( 5 ) is held by each land portion ( 21 ) with a pressure.

This application is a continuation of applications Ser. No. 09/127,917filed Aug. 3, 1998 now U.S. Pat. No. 6,142,761.

BACKGROUND OF THE INVENTION

The present invention relates to an optical disc molding apparatus usedto mold a base of a disc such as an audio disc (CD (compact disc)), avideo disc or the like, and more particularly relates to an optical discmolding apparatus in which an outer peripheral portion of a disk basemay be protected from being deformed into a trumpet shape by improving ashape of a ring forming the outer peripheral portion of the disc base,resulting in a disc base of a high quality being obtained.

Heretofore, as optical recording media such as an audio disc, a videodisc and so on for recording a variety of information, there are knownoptical recording media (hereinafter collectively referred to as“optical disc”) for recording information by irradiation of recording orreproducing light. Such an optical disk generally includes aninformation recording layer. As a method of forming an informationrecording layer having very fine concavities and convexities such asphase bits, pregrooves and so on in which a variety of information suchas data information, a tracking servo signal and so on is recorded,there has hitherto been used an injection molding method using astamper.

FIG. 1 of the accompanying drawings is a cross-sectional viewillustrating the mold clamping state of a metal molding apparatus formolding a disc base of an optical disc. In FIG. 1, reference numeral 1generally denotes a stationary side die. In this stationary die 1, thereis assembled a stationary metal mold 2 the side of which opposes acavity is mirror-polished. Reference numeral 3 denotes a movable diewhich may be moved up and down relative to the stationary die 1 along astay, not shown. Similarly, a movable metal mold 4 the side of whichopposes the cavity is mirror-polished is assembled into the movable die3. Cooling water paths 2a, 4a are defined in the stationary metal mold 2and the movable metal mold 4, respectively,

A stamper 5 is disposed on the cavity surface side of the stationarymetal mold 2 to transfer and mold a signal pit on the disc. The stamper5 is held by a ring 6 which is served as also a metal mold for moldingan outer peripheral portion of the disc.

More specifically, the ring 6 is formed such that the outer peripheralportion of the stamper 5 is urged against the cavity surface side of thestationary metal mold 2 by a land portion 8 of a convex shape formed onthe upper edge of the innermost peripheral portion of an innerperipheral portion 7 of the ring 6. A thick outer peripheral portion 9of the ring 6 is fixed to the stationary metal mold 2 by a plurality ofbolts 10.

The movable die 3 is fitted into the ring 6 in such a manner that anouter peripheral surface of the movable metal mold 4 is brought incontact with the inner peripheral surface of the ring 6. Thus, thestationary metal mold 2, the movable metal mold 4 and the ring 6constitute a molding cavity 11.

In this clamping state, as shown in FIG. 2 in an enlarged-scale, theland portion 8 of the inner peripheral portion 7 and the stamper 5 havea clearance C1 therebetween, the outer peripheral surface of the outerperipheral portion 9 and the stationary side die 1 have a clearance C2therebetween, and the inner peripheral portion 7 and the movable metalmold 4 have a clearance C3 therebetween, respectively. The clearances Cland C3 are set to be such clearance values as to pass only a gas withinthe cavity 11 but to inhibit a molten resin filled into the cavity 11from entering, e.g. tens or more micrometers. The clearance C2 is set tobe several micrometers, for example.

On the other hand, as shown in FIG. 1, the stationary side metal mold 2has at its center attached a sprue 13 through a sprue bush 12 from theside of the stationary die 1. This sprue 13 has at its center defined aninjection orifice 14 to inject a molten resin into the above-mentionedcavity 11. In FIG. 1, reference numeral 15 designates a nozzle guide forpositioning an injection nozzle (not shown) against the sprue 13.

Moreover, the movable metal mold 4 has at its center attached a sleeve17 through a bush 16 from the side of the movable die 3. A gate-cutpiston 18 is disposed within the sleeve 17.

A manner in which an optical disc is molded by this prior-art opticaldisc molding apparatus will be described next.

Under the condition that the injection nozzle (not shown) is positionedat the sprue 13, a molten resin is injected from the injection nozzlethrough the injection orifice 14 into the cavity 11 and thereby filledinto the cavity 11. As the molten resin is filled into the cavity 11, agas which is in the gaseous state within the cavity 11 is escaped from aclearance (portion of the clearance C1) formed between the ring 6 andthe stamper 5 and a clearance (portion of the clearance C3) formedbetween the ring 6 and the movable metal mold 4 so that the outerperipheral shape of the disc is finally molded by the ring 6. Then,after a predetermined time elapsed since the filling of the molten resinhas been completed, the gate-cut piston 18 is elevated so that, at thesame time the gate of the injection orifice 14 is cut out, a disccenter-hole is molded by the outer peripheral portion of the gate-cutpiston 18.

After the disc is cooled and cured, the movable die 3 is loweredtogether with the movable metal mold 4 and a molded disc base isobtained.

A molten resin 19 injected into the cavity 11 is filled into the cavity11 at a high temperature (about 330° C.) with a large pressure of 1000kg/cm² (1 ton). Due to such large filling pressure, the ring 6 whichmolds the outer peripheral portion of the disc base is swollen towardthe outer diameter side by the amount of the clearance C2 as shown by aphantom line in FIG. 2, and in particular, the inner peripheral portion7 of the ring 6 is buckled and deformed toward the stamper 5 side.

A stress produced in the ring 6 is a stress obtained when the ring 6 isreturned to the original position after the resin pressure decreases asthe resin is cooled and cured since the filling of the molten resin hasbeen completed. A study of simulation results obtained by the assigneeof the present application reveals that swollen portions 20 a, 20 b of atrumpet shape are produced on the upper and lower surfaces of the outerperipheral edge portion of a disc base 20 by the above stress as shownin FIG. 3. The swollen portion of the trumpet shape on the upper surfaceof the disc base 20, i.e. the swollen portion 20 a on the signal pitside is swollen higher than the swollen portion 20 b on the read-outside of the lower surface of the disc base 20.

As one of methods for preventing the ring 6 from being buckled, theremay be considered a method of holding the'stamper 5 with the wholesurface of the inner peripheral portion 7 of the ring 6. According tothis method, although the buckled and deformed state of the ring 6 dueto the filling pressure may be avoided, the outer peripheral portion ofthe stamper 5 is pressed down completely. There is then the problem thatthe stamper 5 is curved toward the cavity 11 side by an amount obtainedwhen the stamper 5 is thermally expanded by the molten resin which is ata high temperature upon injection.

Further, there is a disadvantage that a burr tends to be produced in theouter peripheral portion of the molded disc base by a stress obtainedwhen the ring 6 is returned to the original position.

Furthermore, there arises a problem that optical of optical disc aredeteriorated by a birefringence produced in the outer peripheral portionof the molded disc due to the stress obtained after the ring 6 wasreturned to the original position.

SUMMARY OF THE INVENTION

In view of the aforesaid aspect, it is an object of the presentinvention to provide an optical disc molding apparatus capable ofmolding an optical disc in which the occurrence of a swollen portion oftrumpet shape on the outer peripheral portion of a disc base may beminimized.

It is another object of the present invention to provide an optical discmolding apparatus capable of molding an optical disc in which theoccurrence of a burr on the outer peripheral portion of a disc base maybe avoided.

In order to attain the aforesaid objects, according to the presentinvention, there is provided an optical disc molding apparatus whichincludes a ring for molding an outer diameter portion of a disc base ona molding metal mold and holding a stamper for molding a signal pit. Inthis optical disc molding apparatus, a plurality of grooves are formedon a holding surface of the ring for holding the stamper, and the outerperipheral surface of the stamper is held by the convex portion thereof.

According to the above-mentioned ring, the ring may be prevented frombeing buckled and deformed. As a result, a stress obtained when the ringis returned to the original position can be eliminated and the swollenportion of trumpet shape on/the disc base may be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an optical disc molding apparatusaccording to the prior art;

FIG. 2 is a cross-sectional view showing a ring and portions lyingaround the ring in an enlarged-scale;

FIG. 3 is a cross-sectional view showing the manner in which a-swollenportion of trumpet shape is produced on a disc base;

FIG. 4 is a cross-sectional view showing a clamping state of an opticaldisc molding apparatus according to the present invention;

FIG. 5A is a fragmentary plan view showing a configuration of a landportion;

FIG. 5B is a cross-sectional view taken along the line a—a in FIG. 5A;

FIG. 6 is a cross-sectional view showing a ring and portions lyingaround the ring in an enlarged-scale;

FIG. 7 is a plan view showing the state presented before the ring isengaged with the stationary side die;

FIG. 8 is a plan view showing the manner in which the ring is engagedwith the stationary side die;

FIG. 9A is a fragmentary plan view illustrating in an enlarged-scale thestate presented during the ring is being engaged with the stationaryside die;

FIG. 9B is a fragmentary plan view illustrating the manner in which thering is engaged with the stationary side die;

FIG. 10 is a cross-sectional view showing a ring of another land portionand portions lying around the above-mentioned ring in an enlarged-scale;

FIG. 11A is a fragmentary plan view showing a further modified exampleof the land portion; and

FIG. 11B is a cross-sectional view taken along the line b—b in FIG. 11A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of the optical disc molding apparatus according to thepresent invention will hereinafter be described with reference to thedrawings.

FIG. 4 is a cross-sectional view illustrating the clamping state of thedisc molding apparatus according to the present invention. In FIG. 4,elements and parts identical to those of FIG. 1 are marked with samereference numerals.

In FIG. 4, there is die 1. In this stationary side die 1, there isassembled the stationary side metal mold 2 where the side which opposesthe cavity 11 is mirror-polished. The movable die 3 is provided suchthat it may be moved up and down relative to the stationary side die 1along a stay, not shown. Similarly, the movable metal mold 4 the side ofwhich opposes the cavity 11 is mirror-polished and is assembled into themovable die 3. The cooling water paths 2 a, 4 a are defined in thestationary side metal mold 2 and the movable metal mold 4, respectively.

The stamper 5 is disposed on the cavity surface side of the stationaryside metal mold 2 to transfer and mold a signal pit onto a disc. Thestamper 5 is held by the ring 6 which also serves to mold an outerperipheral portion of the disc.

More specifically, the upper surface of the inner peripheral portion 7of the ring 6 according to the present invention is formed as anirregular surface. According to this embodiment, as shown in FIGS. 5Aand 5B, this irregular surface comprises a plurality of concentric landportions 21 and a plurality of concentric groove portions 22 which areformed alternately. Each groove portion 22 includes a communicatinggroove 22 a, and this communicating groove 22 a has a gas escape hole 23defined which passes through the inner peripheral portion 7 of the ring6. Under the condition that each land portion 21 urges the outerperipheral portion of the stamper 5 against the cavity surface side ofthe stationary side metal mold 2, the thick outer peripheral portion 9was fixed to the stationary side metal mold 2 by a plurality of bolts10.

The movable die 3 is engaged with the above-mentioned ring 6 in such amanner that the outer peripheral surface of the movable metal mold 4 isbrought in contact with the inner peripheral surface of the ring 6.Thus, the stationary side metal mold 2, the movable metal mold 4 and thering 6 constitute the molding cavity 11.

Under this clamping state, as shown in FIG. 6 in an enlarged-scale, thering 6 is accurately worked in such a manner that the clearance C1 ishardly produced between each land portion 21 on the inner peripheralportion 7 and the stamper 5 and they are strongly urged each other byfastening the bolts 10 firmly. Also, the outer peripheral surface of theouter peripheral portion 9 and the stationary side die 1 are closelycontacted with each other in such a manner that the clearance C2 willnot be produced. The clearance C3 between the inner peripheral portion 7and the movable metal mold 4 can be ten or more. As a result, most ofgas within the cavity 11 may be exhausted to the outside of the cavity11 from the clearance C3, and the molten resin 19 filled into the cavity11 may not enter the clearance C3.

On the other hand, as a method of closely contacting the outerperipheral surface of the outer peripheral portion 9 with the innerperipheral surface of the stationary side die 1 in such a manner thatthe clearance C2 will not be produced, according to the presentinvention, there is used an arrangement shown in FIGS. 7 and 8.

As illustrated in FIGS. 7 and 8, concave portions 24 are formed on theinner peripheral surface of the stationary side die 1 at an equal pitch,and the inner wall surfaces of the stationary side die 1 except theconcave portions 24 are used as engagement surfaces 25. On the otherhand, concave portions 26 are formed on the outer peripheral surface ofthe ring 6 in an opposing relation to the engagement surfaces 25 of thestationary side die 1, and outer peripheral surfaces of the ring 6except the concave portions 26 are used as engagement surfaces 27. Then,both of the engagement surfaces 25, 27 are closely contacted with eachother and thereby engaged with each other. To this end, as shown inFIGS. 9A, 9B in an enlarged-scale, both of the engagement surfaces 25,27 are formed as wedge-like shape such that both of the engagementsurfaces 25, 27 are closely engaged with each other when the ring 6 isrotated. Accordingly, the ring 6 is clamped to the inner peripheralsurface of the stationary side die 1 and then fixed by the bolts 10.

Turning back to FIG. 4, the stationary metal mold 2 has at its centerfixed the sprue 13 through the sprue bush 12 from the side of thestationary die 1. The sprue 13 has at its center defined the injectionorifice 14 to inject the molten resin 19 into the above-mentioned cavity11. Similarly, there is provided the nozzle guide 15 which is used toposition the injection nozzle (not shown) against the sprue 13.

Moreover, the movable metal mold 4 has at its center attached the sleeve17 through the bush 16 from the side of the movable die 3. The gate-cutpiston 18 is disposed within the sleeves 17.

A manner in which an optical disc is molded by an optical disc moldingapparatus according to the present invention will be described below.

Under the condition that the injection nozzle (not shown) is positionedat the sprue 13, a molten resin is injected from the injection nozzlethrough the injection orifice 14 into the cavity 11 and thereby filledinto the cavity 11. As the molten resin is filled into the cavity 11,most of gas which is in the gaseous state within the cavity 11 isescaped from a clearance (portion of the clearance C3) formed betweenthe ring 6 and the movable metal mold 4, and a part of gas is escapedfrom a clearance (portion of the clearance C1) formed between the ring 6and the stamper 5, and exhausted through the groove portion 22 from thegas escaping hole 23. Then, finally, the outer peripheral shape of thedisc is molded by the ring 6. Then, after a predetermined time elapsedsince the filling of the molten resin has been completed, the gate-cutpiston 18 is elevated so that, at the same time the gate of theinjection orifice 14 is cut, the disc center-hole is molded by the outerperipheral portion of the gate-cut piston 18.

After the disc is cooled and cured, and the movable die 3 is lowered andreleased together with the movable metal mold 4 and a molded disc baseis obtained.

The molten resin 19 injected into the cavity 11 is filled into thecavity 11 with a high pressure of 1000 kg/cm² (1 ton) as mentionedbefore. Therefore, according to the ring 6 of the optical disc moldingapparatus according to the present invention, since the concentric landportions 21 formed over the whole upper surface of the inner peripheralportion 7 of the ring 6 are urged against the stamper 5 to hold thestamper 5, a filling pressure of molten resin 19 is dispersed into eachland portion 21 to produce a stress. As a consequence, the innerperipheral portion 7 may be avoided from being buckled and deformed.Moreover, since the clearance between the outer peripheral portion 9 andthe stationary side die 1 is removed, it is possible to prevent the ring6 from being swollen toward the outer diameter side due to the fillingpressure.

As described above, there is produced no stress when the ring 6 isreturned to the original position after the disc base was molded.Accordingly, the swollen portions of trumpet shape on the upper andlower surfaces of the outer peripheral edge portion of the disc base maybe minimized. Also, there may be molded a disc base in which abirefringence or a burr is difficult to be produced on the outerperipheral portion of the disc base.

Moreover, since each of the land portions 21 is urged against thestamper 5, the stamper 5 is not completely pressed but is held with aproper pressing force, thereby avoiding such a phenomenon where thestamper 5, which was thermally expanded when the molten resin wasfilled, is moved relative to the ring 6 with a friction and as aconsequence, the stamper 5 is curved to the cavity 11 side.

Further, since the ring 6 is engaged with the stationary side die 1 in awedge fashion when the ring 6 is rotated as the arrangement in which thering 6 is engaged with the inner peripheral surface of the stationaryside die 1 without clearance, there may be obtained the engagement statewithout clearance by a simple arrangement without requiring assembliesof high accuracy

The present invention is not limited to the aforementioned embodimentand may be variously modified without departing from the gist of thepresent invention.

FIG. 10 shows an arrangement in which a clearance C4 of 2 to 5 μm isproduced between only the innermost peripheral land portion of the ring6 and the stamper 5 and the other land portions 21 are closely contactedwith the stamper 5 similarly as described above. Thus, when the moltenresin 19 is filled into the cavity 11, a gas may be effectivelyexhausted also from the clearance C4. In that case, since the clearanceC4 lies in a range of from 2 to 5 μm, a burr may be prevented from beingproduced on the disc base.

Further, the shape of the land portion is not limited to the concentricshape, and may be a spiral land portion. In addition, as shown in FIGS.11A and 11B, if the inner most peripheral land portion may be left asthe concentric land portion 21 and other remaining land portions 28 maybe formed as land portions which are arrayed radially, then thesupporting function of the stamper 5 may be obtained similarly asdescribed above.

Furthermore, the disc base molded by the optical disc molding apparatusaccording to the present invention is suitably applied to a disc base ofa CD, a DVD, a DVD-ROM and so on or the optical disc molding apparatusof the invention is suitably applied to a molding apparatus for moldinga disc base such as a disc base of a next-generation mass-storageoptical disc which will be commercially available in the near future orthe like.

As described above, according to the optical disc molding apparatus ofthe present invention, in the ring for molding the outer peripheralportion of the disc and which also serves to hold the stamper, aplurality of concave and convex surfaces are formed on the holdingsurface thereof for holding the stamper and the outer peripheral surfaceof the stamper is held by the convex surface, whereby the occurrence ofthe swollen portions of trumpet shape on the upper and lower surfaces ofthe outer peripheral edge portion of the disc base may be minimized. Inaddition, there may be molded a disc base in which a birefringence or aburr is difficult to be produced on the outer peripheral portion of adisc base.

Furthermore, since each land portion is urged against the stamper, thestamper may be held with a proper pressing force. Thus, when the moltenresin is filled into the cavity, the stamper may be prevented from beingcurved to the cavity side.

Having described preferred embodiments of the invention with referenceto the accompanying drawings, it is to be understood that the inventionis not limited to those precise embodiments and that various changes andmodifications could be effected therein by one skilled in the artwithout departing from the spirit or scope of the invention as definedin the appended claims.

What is claimed is:
 1. An optical disc molding apparatus comprising: apair of dies where one of said dies is movable relative to the otherdie, which remains stationary; a pair of metal molds for forming acavity therebetween; a stamper for transferring an information pit on adisc; and a movable, rotatable ring closely attached to said metal moldsand said stationary die, having a holding surface for holding saidstamper, said holding surface having a plurality of grooves and holdingan outer peripheral surface of said stamper with convex surfaces of saidgrooves and molding an outer peripheral surface of said disc.
 2. Anoptical disc molding apparatus as claimed in claim 1, wherein saidplurality of grooves of said ring are concentric in shape.
 3. An opticaldisc molding apparatus as claimed in claim 1, wherein said plurality ofgrooves of said ring are spiral in shape.
 4. An optical disc moldingapparatus as claimed in claim 1, wherein said plurality of grooves ofsaid ring are radial in shape.
 5. An optical disc molding apparatus asclaimed in claim 1, wherein said ring is urged against an inner diametersurface of a metal mold to which an outer diameter surface of said ringis attached in such a manner that said ring and said inner diametersurface have no clearance produced therebetween.
 6. An optical discmolding apparatus as claimed in claim 5, wherein one of said dies has onits one inner peripheral surface formed concave and convex portions,said ring has on its outer peripheral surface formed concave and convexportions and said ring is attached to said die and said metal mold byengaging said concave and convex portions with each other.
 7. An opticaldisc molding apparatus as claimed in claim 6, wherein said convex andconcave portions are formed to be a wedge shape.
 8. An optical discmolding apparatus as claimed in claim 2, wherein said ring has on itsupper convex surface of innermost peripheral side a clearance formedbetween it and said stamper.
 9. An optical disc molding apparatus asclaimed in claim 8, wherein said clearance lies in a range of from 2 to5 μm.